The present invention relates in general to a grinding mill, and more particularly to a grinding mill with removable grinding rolls.
It is well known to those conversant with this art that high requirements as to dimensional accuracy and tolerance limitations are made of the grinding rolls used in grinding mills. This is, in fact, true not only of these factors, but also with respect to the position of the grinding rolls in the grinding mill. It is clear that if these requirements are not met, the action of the grinding rolls will not be satisfactory. Because of the requirements made of the dimensional accuracy of the grinding rolls, the latter must be frequently disassembled from the grinding mill, machined (e.g. re-ground) and reinstalled.
The grinding rolls can be mounted in the grinding mill in one of two ways, either by means of undivided journals or bearing bodies, or by means of bi-partite journals or bearing bodies. The use of undivided bearing bodies has the disadvantage that when the grinding rolls have to be removed, the bearing bodies themselves must also be removed, and subsequently each grinding roll with its bearing bodies must be re-installed, whereupon the bearing bodies must be adjusted until they are in the proper position to thereby assure that the grinding roll also assumes the proper position, a time-consuming and expensive operation which may require hours of work to complete.
For this reason the prior art generally prefers the use of bi-partite bearing bodies in order to hopefully eliminate much of the adjusting work. These bearing bodies have two sections one of which is firmly and permanently mounted in the grinding mill, whereas the other section is removable when a grinding roll is to be disassembled from the grinding mill. When the grinding rolls are subsequently to be reinstalled, their trunnions are inserted into the fixed bearing section and the removable bearing section is then re-installed to form a complete bearing body together with the fixed bearing section. The fixed bearing section is precisely positioned, often with a tolerance of only a few hundredths of a millimeter, and it is clear that to properly position the trunnions of one of the grinding rolls --which latter may weigh hundreds or even thousands of kilograms-- under these circumstances is a very difficult and highly skilled undertaking. The slightest error can result in significant damage to the grinding roll, the bearing or the bearing body, and all of this is constantly accompanied by the danger that the grinding roll might slip during the adjustment and might cause even worse damage or possibly an injury to the workers. This is all the more true as in many instances where such grinding mills are used, for example in oil mills, fodder mills and the like, the use of heavy overhead cranes for holding and manipulating the grinding rolls is impossible because of the required large number of vertical conduits which extend upwardly from or downwardly to the grinding mill and which physically preclude the use of an overhead crane. For this reason it is necessary to use block and tackle and similar devices for lifting the grinding rolls out of their journals and replacing them in the journals, and to hold them during the adjustment, which latter operation requires still additional tools. All in all, the use of bi-partitie journals has also not been very satisfactory in the prior art.
To summarize the state of the art, it can be pointed out that if the grinding rolls are journalled in undivided journals, the installation and removal of the grinding rolls together with their journals is quick, but the adjustments required for the journals after installation is extremely time-consuming and difficult. If bi-partite journals are used for the grinding rolls, then the installation and removal is also relatively quick, but the actual insertion and removal of the grinding roll trunnions with reference to the associated journals is time-consuming and connected with great difficulties, because it requires so high a precision that this work can be carried out only very slowly and with great skill. Added to this is the fact that there is an ever-present possibility of accident, for reasons which have been explained above.